The trains of the game are in fact 3D models processed with specific softwares to which they are applied texture, if you a search in the forum you'll find something.
Why not contact someone able in this work I will suggest Rodea2007 I like his work.

Renothian wrote:Ya ok but even the official page for Sid Meier's Railroads says it has an in game loco builder, where is that? I can not find it anywhere ?!?

Gee, I've been involved with the game for quite some time and I've not heard of this; even went to the official page to check (http://www.2kgames.com/railroads/railroads.html) and sure enough, nary a word!
Several folks here Do make their own locos, search through the forum and you will find lots of info.

BTW, there is an in-game map editor. It can be enabled after patch 1.10 is applied (the only official patch).

yes it is easy to built own Models you ned skills at 3dsmax or Blender

i'am working on the same model as rodea did few years ago
it is an bi level Passenger Car other wise you can look at Bobby's smr Forum there are so many models like Gondolas; Double Stack Container;Trailer Cars; Grain Cars; Coal Cars; Box Cars and Reefers and a lot of engines

just a few examples of my Painted Rock Island Stock and iam currently working on an remade of rodea's grain car:

Renothian wrote:Ya ok but even the official page for Sid Meier's Railroads says it has an in game loco builder, where is that? I can not find it anywhere ?!?

Gee, I've been involved with the game for quite some time and I've not heard of this; even went to the official page to check (http://www.2kgames.com/railroads/railroads.html) and sure enough, nary a word!
Several folks here Do make their own locos, search through the forum and you will find lots of info.

BTW, there is an in-game map editor. It can be enabled after patch 1.10 is applied (the only official patch).

Old marketing material prior to smr's launch was more misleading. The old material implied a complete train maker inside the game.

It is possible that during development they were more enthusiastic about modding. Who knows maybe they were even experimenting with a basic train customizer. This was around when Spore was being hyped and web "2.0" so user generated content was a popular buzzword. They might have accidentally told someone from marketing about the experiment.

More likely marketing were the ones over enthusiastic and simply over sold the colour picker.

The manual is incredibly useful, even though it is only 5 pages long (see screenshots for examples). The same principles apply to industries, train cars, houses, etc, so you can see the potential.

The only part I would disregard is on page four, where it says to put the new assets into the "CustomAssets" folder, because that is asking for trouble. Include them in the "UserMaps" folder instead, works just fine.